Why It Matters

Battery saver: The radio transmitter chip shown in this mock-up adjusts voltage on the fly, slashing demand for electricity.

Beyond the glitz of the International Consumer Electronics Show, the wireless industry faces a fundamental problem: more features and faster data transmission are draining phones’ batteries faster than ever.

Fortunately, there’s room for improvement inside the devices, in parts known as power amplifiers that turn electricity into radio energy. In phones, they typically consume more power than any other component but waste half of it along the way, as lots of people can attest if they’ve watched their battery die (and their phone get warm) after an hour of streaming video. The same problem bedevils wireless networks’ base stations, which send and receive signals to and from individual phones.

Now a major effort is under way to develop smarter power amplifiers that significantly reduce waste. Eta Devices, an MIT spinoff based in Cambridge, Massachusetts, is preparing a base station module and a chip that it says not only decrease battery drain but work well in high-bandwidth applications for 4G LTE and future ultrafast technologies.

The fundamental problem is that the power needed for radio output fluctuates rapidly when a device is transmitting data at high rates. Existing power amplifiers maintain their voltage at a fairly high level at all times to be prepared for peak needs—but this is wasteful. Newer approaches adjust that level on the fly, following the “envelope” of the actual radio signal.

Such “envelope tracking,” or ET, technologies are the hottest hardware development in the mobile-phone industry. Last fall Qualcomm became the first company to ship a chip with such technology, which it says is the industry’s first for 3G and 4G LTE mobile devices.

The company says the chip helps lower electricity consumption by 20 percent and helps reduce a related problem—heat generation—by up to 30 percent, “allowing for longer battery life for end users, as well as enabling manufacturers to shrink the size of their devices,” says Peter Carson, Qualcomm’s senior director of marketing.

The difficulty with ET, though, is that its efficiency plunges at higher data rates. Envelope trackers often require a relatively large capacitor to store and release bursts of energy while maintaining smooth and continuous voltage changes.

Eta Devices takes a radically different approach, favoring fast, abrupt changes with a smaller capacitor. Using a smaller capacitor is more efficient; the downside is that the changes in energy cause more noise in a wireless signal. That problem is overcome by cutting-edge digital signal processing, says Joel Dawson, one of two MIT electrical engineering professors who cofounded the company.

Mattias Åström, the company president, reaches for an automotive analogy to compare the two approaches. “Envelope tracking is basically a continuous variable transmission, compared to our manual gearbox,” he says. “Fuel consumption is always better when you have a manual gearbox.”

The company’s work hasn’t been published and the chip is now being fabricated for the first time, but the concept has been built out for base stations and may be commercialized this year. The Eta module, a little smaller than a shoebox, is the first 4G LTE transmitter in the world to achieve average efficiency greater than 70 percent, a big jump from the 45 to 55 percent in currently available technology, says Dawson.

Vanu, a company that makes low-power wireless base stations (see “A Tiny Cell-Phone Transmitter Takes Root in Rural Africa”), is testing the technology and may become an early customer. “We think this can give us a ‘green’ benefit as well as an operating cost advantage,” says David Bither, direct of platform engineering at Vanu.

The result could be to expand connectivity and make it affordable to more people in the developing world, where expensive diesel fuel powers at least 640,000 remote base stations at a cost of $15 billion.